A roll-and-press lighter typically comprises a lighter body containing a reservoir of pressurized fuel, a valve for releasing fuel from the reservoir to a burner nozzle, a lever for operating the valve, and a rotatable wheel assembly comprising a sparkwheel and a pair of thumbwheels. A flint is mounted on the lighter body so that it presses against the sparkwheel, and a metal windshield is usually arranged around the burner.
Such lighters are commonly used as cigarette lighters, and derive their name from their operating procedure. In order to operate the lighter the typical user first rolls the wheel assembly by drawing his thumb rapidly across the thumbwheels. The end of the lever opposite the valve is provided with a pad which is positioned to receive the user's thumb as it falls off the wheel assembly at the end of its stroke. By pressing down on this pad the user opens the valve to release fuel to the burner, where it is ignited by sparks produced by friction between the flint and the rotating sparkwheel.
In order to reduce accidents and comply with national legislation, a wide variety of mechanisms have been proposed for making such lighters child resistant, which is to say, substantially inoperable by children of less than five years of age. In practice the child resistance of a lighter is established by empirical testing by a group of children of less than five years of age in accordance with the relevant Rules and Regulations of the United States Consumer Product Safety Commission.
It is essential that a child resistant lighter should always return automatically to the safe condition whenever it is released by the user. Some known lighters are designed to be manipulated to a stable, enabled condition in a first, enabling step, so that a second, ignition step may then be carried out, after which the lighter resets automatically to the safe condition. Since such lighters are capable of being left inadvertently in the enabled condition for an indeterminate length of time, after which the lighter may be ignited without any further child-resisting impediment, they are no longer considered to meet this essential criterion.
Examples of such lighters include U.S. Pat. No. 6,102,689, which discloses a roll-and-press lighter with a catch which normally prevents depression of the lever; and EP0611096 A2, U.S. Pat. Nos. 5,271,731, 6,095,795, 5,324,193, and 5,704,776, which all disclose roll-and-press lighters in which either the lever or an element attached to the lever normally engages the lighter body so that it cannot be depressed. In order to release the lever and ignite the lighter, the user must first push the catch or lever or other element to a stable, intermediate position, in which it is retained by a corresponding engaging formation on the lighter body. The lighter remains in this intermediate condition until the user rotates the wheel assembly and depresses the lever in a second, conventional roll-and-press action, which ignites the lighter without any further child-resisting impediment.
In order to operate a roll-and-press lighter, it is essential that the lever is depressed to release gas to the burner as soon as the sparkwheel has been rotated and before the sparks produced by its rotation against the flint have time to decay. This is accomplished by the rapid roll-and-press operation which is familiar to users of this type of lighter. For this reason it would be difficult or impossible in practice to ignite the last described lighters by applying both inward and downward forces to the lever pad in a single operation after rotating the wheel assembly, and without first setting the locking mechanism to the stable, intermediate position. Since the stable intermediate position is therefore an essential requirement for such lighters to operate, locking mechanisms of this last mentioned class are considered unsuitable for use in a modern child resistant lighter.
In addition to the requirement for automatic reset, it is important that a child resistant lighter should be easily operable by the adult user without undue effort and inconvenience, while offering a high level of resistance to operation by children. Since disposable roll-and-press lighters are manufactured in large numbers and sold at very low cost, it is also important that the costs of materials, assembly and tooling are minimized.
U.S. Pat. No. 5,971,748 and WO01/38795 A1, both to the present applicant, disclose roll-and-press lighters having mechanisms for preventing depression of the lever, but which avoid the need for a stable, intermediate position of the mechanism by providing for the wheel assembly to engage the mechanism and move it to the enabled position as it rotates. When the user applies sufficient force to the wheel assembly, the lever is released so that it can then be immediately depressed by the user's digit.
Although these last mentioned lighters automatically return to the safe condition whenever they are released by the user, they incur the disadvantage that, since the child resistant mechanism is released only by applying force to the wheel assembly, they may not prevent a child from releasing the mechanism by rolling the knurled thumbwheels along the floor. Moreover, in use, the periphery of the wheel assembly is repeatedly rotated at high speed against the mechanism. The resulting wear tends to increase the force required to release the mechanism, making the lighter more difficult for the adult user to operate.
Many prior art lighters have incorporated safety catches which normally block operation of the lever or wheel assembly and which must be manipulated to an unblocking position prior to ignition of the lighter. Such catches are often necessarily small and fiddly to operate and make the lighter more difficult for adults to use. They can also require substantial changes to the lighter body, necessitating extensive and costly re-tooling. Moreover, in some lighters the method of operation of the safety catch may be evident to the observant child, and the lighter may then be vulnerable to operation by imitation of the actions of the adult user.
For all of these reasons it is therefore preferred not to provide the lighter with a separate safety catch which is directly operable by the user, but instead to alter the operating characteristics of the lighter so that it is inherently inoperable by a small child.
This approach is exemplified by JP 2002048341A, which provides a leaf spring beneath the depressible pad of the operating lever so as to increase the force required to depress the lever. Analogous mechanisms are also known in other types of lighter. For example, U.S. Pat. No. 5,971,751 discloses a piezoelectric lighter which has a resiliently compressible, pressure absorbing device arranged below the operating cap so as to increase the force required to depress it. U.S. Pat. No. 2,498,377 discloses a geared type lighter in which the sparkwheel is rotated by a depressible operating cap; the cap is mounted on a sprung stem which is provided with a latch device with a lip which engages the lighter body. The user must apply sufficient pressure to the operating cap to disengage the lip from the lighter body, which releases the operating cap for rapid downward motion and so ensures reliable ignition.
In each of these lighters the user is required to apply a heavy initial pressure in order to achieve ignition, and the roll-and-press lighter of JP 2002048341A requires the user to maintain this pressure in order to maintain the flow of gas and hence the flame. In practice however many users find it uncomfortable or even impossible to apply the additional pressure required to ignite such a lighter and keep it burning.
U.S. Pat. No. 5,947,715 discloses a roll-and-press lighter in which a projection extends downwardly from the underside of the depressible pad on the lever. The projection has an inclined lower surface which abuts a resiliently biased leg housed in a cavity below the lever. When an adult user applies sufficient pressure to the pad, the leg is forced aside by the inclined lower surface of the projection, allowing the lever to be depressed. Alternatively the leg may incorporate a user operable safety catch, in which case a separate spring means may be used.
This lighter enjoys the advantage that, after the user has applied an initial force sufficient to disengage the corresponding abutting surfaces, less force is then required to maintain the lever in the depressed position. However, the additional components may substantially increase production and assembly costs, especially since the additional components must be inserted into the cavity before assembly of the lever, which substantially complicates the assembly procedure. The child resistant mechanism also requires a relatively large cavity beneath the lever, which reduces the capacity of the fuel reservoir as well as requiring substantial re-tooling for production of the upper part of the lighter body as well as the lever.
U.S. Pat. No. 6,099,297 discloses a roll-and-press lighter having a comparable arrangement wherein a resilient leg extends downwardly from the underside of the depressible pad of the lever into a cavity in the lighter body. The lower end of the leg normally engages the curved upper surface of a block which is fixed to the lighter body. When the adult user applies sufficient force to the pad, the lower end of the leg is forced to one side so that it slides off the block, allowing the lever to move downwards so as to open the valve. The resilient leg is necessarily of substantial length and thickness, and like the lighter of U.S. Pat. No. 5,947,715 requires substantial re-tooling of the lighter body as well as the lever.
In both of the last mentioned lighters, the child resistance of the lighter depends critically on the ability of the resilient leg to return to the safe position after each actuation. In each case the leg must be sufficiently rigid to withstand the force which a small child may apply to the lever without buckling or collapsing. At the same time it must be sufficiently resilient to move aside so as to permit depression of the lever when the predetermined amount of force is applied by the adult user.
In practice it is difficult to balance these properties so as to achieve a consistent minimum actuation force in production. Moreover, repeated flexing of the leg during the lifetime of the lighter may result in permanent, plastic deformation which although slight is sufficient to alter the child resistance of the lighter beyond its designed parameters.
In an alternative approach, WO 99/46539 discloses a roll-and-press lighter wherein a resiliently biased ignition button is housed below the depressible pad of the lever. Rather than engaging the lever, the button protrudes through a hole in the lever so as to directly engage the user's thumb.
Since the ignition resistance button is biased by means of a coil spring, it provides a resistance to the user's thumb which can be expected to remain constant throughout the lifetime of the lighter. However, in order to maintain the flame, the adult user is disadvantageously obliged to maintain the additional coil spring in compression once the lighter has been ignited. As noted above with reference to the lighter of JP 2002048341A, this is difficult for many users.